Technical Field
Embodiments of the subject matter disclosed herein generally relate to a cable-protecting devices (bend restrictors and/or bend stiffeners) used in marine systems, the cable-protecting devices being configured to ensure quick mounting on a cable.
Discussion of the Background
Marine surveys are methods used for geophysical prospecting, in particular, when seeking gas and oil reservoirs. Such surveys gather information about sedimentary rock formations using seismic signals. The signals are reflected, refracted and/or transmitted at interfaces in the surveyed geological formation where the signal's propagation velocity changes. Signals emerging from the explored geological formation are detected by receivers.
FIG. 1 represents an aerial view of a marine seismic survey system 100. This system is generic in terms of arrangement and equipment, not intended to be limiting. System 100 includes a vessel 110 towing a source 120 made of plural gun source-arrays and a streamer spread (only one streamer being labeled 130), along a sail line S.
In order to tow the source and the streamer spread according to a predetermined data-acquisition geometry, a set of cables connect various pieces of equipment to vessel 110. In this document, the term “cable” encompasses various types of cables from simple ropes or chains to complex structures able to transmit power, pressured fluid, signals and to convey the strength necessary for towing. The set of cables (only some labeled) includes streamer lead-in cables 140 connecting the streamers to the vessel, umbilical cables 150 (only one labeled) connecting source arrays to the vessel, two wide ropes 160 connecting deflectors 170, respectively, to the vessel. Further, cross-line distance ropes 180 limit distances between heads of adjacent streamers, and spur lines 185 limit distances between the left-most and the right-most streamer and the corresponding left-side and right-side deflector. Floats 190 are tied to streamer heads with link ropes (not labeled).
Bend restrictors and/or bend stiffeners are used to limit bending of cables (such as lead-in or umbilical cables) at places where undesirable bending forces often occur. Such places (e.g., A and B in FIG. 1) are where other cables (e.g., cross-line distance ropes, spur lines, cables attaching a float or a depressor, etc.) or equipment is attached to a cable. In these places, the cables are reinforced by bend restrictors and/or bend stiffeners to alleviate the inherent shear and tear. The term “bend stiffener” usually refers in particular to a device is configured to oppose cable bending, while the term “bend restrictor” usually refers to a device configured to limit the bending radius of the cable. In this document, the term “cable-protecting device” encompasses both “bend restrictor” and “bend stiffener.”
Conventionally, helical rods surrounding the cable are used as bend stiffeners. Some bend stiffeners use plural layers. FIG. 2 illustrates a conventional bend stiffener 200, whose main body 210 protects cable 220's integrity, at a cable attachment location (see collar 230 provided for attaching another cable). Main body 210 is split in two parts closed with screws 240 (only few labeled), designed to ensure bend stiffener's grip on the cable and its mechanical properties. Tightening all the screws when mounting this bend stiffener for deployment, and then, removing them after cable's recovery, takes a substantial amount of time.
FIG. 3 illustrates a conventional bend restrictor 300, including plural knuckles 310, 320, . . . , 380 that form a “vertebrae” along cable 390. Collar 395 for attaching chains is mounted over knuckle 350. The knuckles have wider diameters than portions there-between, such as 315 and 325. Cable 390's bending radius is limited by the distance between these sectors. The knuckles are also mounted using screws 305 (only few labeled) and thus the mounting time is substantial.
A recurring problem with conventional bend restrictors and stiffeners is the long time necessary to mount these protective devices on the cables when the equipment is deployed. For example, it takes between 40 min and 2 h to mount a conventional bend restrictor (such as the one in FIG. 2) on a lead-in cable. Several deflectors have to be mounted and removed over bend restrictors at each deployment and recovery of the survey equipment. Additionally, as streamer spreads become wider, mechanical properties of bend stiffeners and/or restrictors need to be improved.
Accordingly, it is desirable to develop bend restrictors and/or stiffeners able to be quickly mounted and to have enhanced mechanical properties.